The invention relates to a process for the production of fine-grained slush of low-boiling gases, such as e.g. nitrogen or hydrogen. Slush is a mixture of liquid and ice, which is at the triple point, in equilibrium with the gas phase.
Because of its good transportation, heat-transfer and storage properties, the slush of low-boiling gases is suited better than the corresponding boiling point liquid, as a refrigerating medium, in particular in the cases, in which a high refrigerating efficiency at a low temperature level is required for a limited period. This is the case, for example, for many physical experiments. However, slush can be used very well also for continuous cooling, e.g. of supraconductors.
Slush of low-boiling gases, has been prepared up to now according to the pumping down process. In such process liquefied, low-boiling gas is in an insulated container. By means of a vacuum pump, gas is continuously pumped out of the gas chamber of the insulated container, which causes a drop in the pressure. Since the liquid has to create the heat of evaporation for the drawn off gas, the liquid cools down. As soon as the triple-point pressure is reached, the ice formation starts.
In such techniques, ice is formed first on the surface. By periodical changing of the suction ability of the vacuum pump, sub-surface ice formation can be initiated, and the mixing of the ice with the liquid to slush can be effected. For a shortening of the process, it is also known to release the boiling-point liquid in a nozzle, arranged in the reservoir, to the triple point pressure, and to initiate subsequently the ice formation by sucking off the gas obtained by means of a vacuum pump.
The object of each slush production for cooling purposes is to reach an ice portion as large as possible in the slush, otherwise the good transportation properties of the slush are impaired in pipe lines. Therefore, it must be aimed at maintaining the ice particles in the slush as small as possible. In the case of the slush production, according to the pumping off process, this goal is not sufficiently reached. In particular in the case of hydrogen, there is formed on the surface ice of a more crystalline structure, and it is often necessary to destroy crystalline formations by stirring, in order to obtain slush with fine-grained ice.